The objective of this research is to explore how school transitions that occur early in the life course affect students'socio-emotional well-being (i.e., psychological functioning and social relationships) and health behaviors, and how disruptions in these domains affect later educational performance. My research will use a sequential mixed-methods design, with an initial quantitative component informing subsequent qualitative inquiry. The quantitative research will draw on three national, longitudinal data sets targeting different stages of the early life course: the Early Childhood Longitudinal Study-Kindergarten Cohort for the transition to full- time schooling, the NICHD Study of Early Child Care and Youth Development for the transition to middle school, and the National Longitudinal Study of Adolescent Health for the transition to high school. Using these datasets, I will address three specific aims: 1) determine racial/ethnic differences in students'socio- emotional well-being and health behaviors across each school transition, 2) identify the school contexts in which disruptions in socio-emotional well-being and health factors-and racial/ethnic differences in these disruptions- are most and least pronounced, and 3) assess how disruptions in socio-emotional well-being and health behaviors during school transitions affect racial/ethnic differences in later educational performance. I will use a number of quantitative analysis techniques (repeated measures, propensity scoring, linear regression, structural equation modeling) to examine transition experiences, the moderating influence of race/ethnicity and school context, and the relationship of transition experiences to distal educational outcomes. Quantitative results will inform the development of a qualitative interview protocol to be used with a diverse sample of 40 students. This qualitative research seeks to identify the specific psychosocial mechanisms by which school transitions can be disruptive to socio-emotional and health functioning for different race/ethnic groups, focusing particularly on differential effects of school transitions for each racial/ethnic group. This research will expand our understanding of how school transitions affect students beyond the well-documented academic challenges. PUBLIC HEALTH RELEVANCE: The expectation is that school transitions will disrupt students'socio-emotional well-being and their health behaviors, and these disruptions will be most pronounced among certain race/ethnic groups. Such research will highlight critical intervention points in students'educational careers and identify specific tools for policy intervention as a way of addressing well-documented racial/ethnic differences in educational attainment that underlie corresponding disparities in income, wealth, fertility, and mortality in the U.S.